On the chance that I may be totally wrong let me suggest the following. In
my opinion you are looking at the wrong information. When you mix a 10 MHz
signal with a signal offset by 1 Hz you are subtracting from a 10 E 7
signal 10 E 7 and as a result get 1 Hz representing 10 E 7. Counting it with a
counter with 1 ns resolution, you in effect get at the last digit 10 E 16.
Obviously some of the last digits are irrelevant due to noise and trigger
error. Using two mixers with the common offset oscillator you want the two
phases to be as close as possible to reduce the noise contribution of the
offset oscillator. That is why you want the phase shift. Measuring the time
difference between the zero crossings in my opinion is not the way to go.
I am inspired by the simplicity of the NBS unit (thank you Corby for the
info) to lay out a PC Board; reading some of the comments I would appreciate
any links to more info on that subject that may make the design more
effective. Any help would be greatly appreciate.
Bert Kehren WB5MZJ
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